What do you mean re-do firefox? Please explain a bit more clearly.

lulu13003 said

I have to re-do Firefox everytime when I turn on computer to watch youtube. And I can't install Flash Player

I meant whenever I turned on Firefox my youtube is gone, I can see youtube pages but I cannot see any videos.

Your system details list shows that you have installed Shockwave Flash plugin. You can verify on the Adobe Flash Players Test Page that the Flash plugin is working and which version you have.

• http://www.adobe.com/software/flash/about/

Do you mean that the Shockwave Flash plugin is disabled and you need to click the Lego block icon or you get the notification that the Flash plugin is enabled?

In case you use "Clear history when Firefox closes" or otherwise clear history:

• do not clear the Site Preferences

• Tools > Options > Privacy > Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" > Settings
• https://support.mozilla.org/kb/remove-recent-browsing-search-and-download-history

Clearing "Site Preferences" clears all exceptions for cookies, images, pop-up windows, software installation, passwords, and other website specific data.

Clearing cookies will remove all specified (selected) cookies including cookies with an allow exception that you would like to keep.

You can inspect and manage permissions for the domain in the currently selected tab via these steps:

• Click the "Site Identity Button" (globe/padlock) on the location/address bar
• Click "More Information" to open "Tools > Page Info" with the Security tab selected
• Go to the Permissions tab (Tools > Page Info > Permissions) to check the permissions for the domain in the currently selected tab

I have not tried this, but take a look at it; Video WithOut Flash {web link} Watch videos without flash